1. Statement of the Technical Field
The inventive arrangements relate to communications systems employing mixed radix conversion. More particularly, the inventive arrangements relate to a method and system for performing a mixed radix ring generation and conversion to produce a random number sequence with chosen statistical characteristics over all equivalence classes of a chosen Galois field GF[P].
2. Description of the Related Art
Communication systems can include ring generators in numerous applications. A ring generator is a simple structure over a finite field that exhaustively produces possible outputs through repeated mapping. The mapping is some combination of an additive and a multiplicative mapping; with irreducible polynomials being ideal. For example, a ring generator includes repeated computations of an irreducible polynomial f(x)=3x3+3x2+x on a finite Galois field GF[11] containing eleven (11) elements. A finite or Galois field GF[P] is a field that contains only a finite number of elements {0, 1, 2 . . . P−1}. The finite or Galois field GF[P] has a finite field size defined by the Galois characteristic P, which is often chosen to be a prime number based on number theoretical consequences. The computations ere typically implemented in digital hardware as lookup table operations, feedback loops, or multiplier structures.
Despite the advantages of such a ring generator, it suffers from certain drawbacks. For example, if the ring generator's Galois characteristic P is chosen to be a prime number (not equal to two), then computation is typically inefficient in a digital (binary) domain. Also, lookup table operations performed in the finite or Galois field GF[P] are memory intensive if the Galois characteristic P is large. Moreover, the ring generator's output values are highly deterministic. As such, knowledge of a mapping and current finite field conditions gives complete knowledge of an output sequence.
One method to mask the output sequence of a ring generator from unintended re-construction is to combine two or more ring generators via algorithms that perform bijective mappings into a larger effective domain. An example of this combination is through the Chinese Remainder Theorem (CRT) when the Galois characteristics of the individual ring generators are mutually prime. Another method is to simply truncate the ring generator output value by performing a mixed-radix conversion from a domain GF[P] to a binary domain GF[2k]. Both of these masking methods partially mask the original sequence, yet they still present statistical artifacts that may be used to re-engineer the sequence values. In cryptology, such an attempt is often called a frequency attack, whereby an individual can obtain partial information of the pseudo-random sequence's mapping and state characteristics through statistical analysis. A common layman's example of this process is the word puzzles that exchange one letter for another. Knowledge of the English language gives partial knowledge that E's are more prevalent than Z's. In effect, the search is reduced from brute force to a more logical one.
In view of the forgoing, there remains a need for a mixed-radix conversion method that is computationally efficient in a digital (binary) domain and does not have any gross statistical artifacts. There is also a need for a ring generator having an implementation that is less hardware intensive than conventional ring generator implementations and yield a pseudo-random number sequence that has chosen statistical characteristics. There is further a need for a ring generator having orbits that appear non-deterministic.